Known in the art are electrolysis or power generation processes carried out in filter-press structures comprising an arrangement of electrochemical cells. The typical elementary electrochemical cell suitable for said processes usually has a reduced thickness in order to minimize the energy consumption. Typically the elementary cell is delimited by two conductive plates enclosing a couple of peripheral sealing gaskets, an ion exchange membrane, a couple of electrodes and a couple of current collectors/distributors. The plates and/or gaskets have holes connecting the anodic and cathodic compartments by means of distribution channels. A multiplicity of elementary cells is generally assembled in a filter-press arrangement to form an electrolyzer or electric current generator. Therefore the electrolyzer or generator is made of a series of bipolar plates, gaskets, membranes, electrodes and current collectors/distributors. In particular the alignment of the holes in the plates and gaskets forms longitudinal ducts which are connected to suitable nozzles positioned at one or both ends of the electrolyzer or generator. The reactants and the reaction products, in some cases mixed with the residual reactants, are fed or withdrawn through these nozzles and ducts. Distribution channels permit feeding the reactants to each elementary cell and withdrawing the products and residual reactants therefrom. An assembly of elementary cells as above is described in the European patent application No. EP 0629015 A1 by the same applicant. These assemblies, typically having a series electrical connection, are put out of operation even if only one of the elementary cells is malfunctioning, that is to say if even only one of the electrodes (for example if the electrocatalytic activity is scarce) or only one of the collectors (for example due to increased electrical resistance caused by improper composition or mechanical characteristics) do not properly work or if holes are present in the membrane. This last occurrence is particularly dangerous as it may lead to mixing of incompatible reactants or products, as it is the case in electric current generators where a hole in a membrane causes mixing of oxygen and hydrogen with the consequent ignition of the mixture caused by the electrocatalytic material applied to the electrodes. Therefore the method for externally short-circuiting a malfunctioning cell, as described in the European patent application No. EP 0629015 A1, solves only partially the problem as it allows the electric current to by-pass the malfunctioning cell but does not eliminate possible inconveniences connected with the mixing of the reactants and/or products in case of damages to the membrane. In fact, reactants and products are in any case present in the elementary cell containing the damaged membrane due to the connection between the cell and the longitudinal feed and withdrawal ducts through the distribution channels. As a consequence, a damaged membrane not only hinders operation of the electrolyzer or generator, as it happens when the electrodes or the current collectors/distributors are defective, but also poses safety problems. In the case of damaged membranes, an efficient repairing method is not found in the prior art. Therefore, it would be necessary to disassemble the electrolyzer or generator, or at least open the same in correspondence of the malfunctioning cell, to remove and replace the damaged membrane. This procedure is extremely delicate as further damages are often caused to elementary cells initially free from defects. Further, from the operating point of view, this procedure is time consuming and therefore economically disadvantageous.
It is an object of the present invention to overcome the drawbacks of the prior art by disclosing an efficient method for repairing malfunctioning elementary cells which permits to restore the best operating conditions of an electrolyzer or electric current generator without any need for opening and replacing the damaged or defective parts.